Left a large glass bowl sitting on a teak garden table last summer,
which unfortunately has left a dark 6" diameter stain on the table
surface, presumably as rainwater with the usual air pollutants has
run off the bowl and settled on the wood before eventually evaporating
away.

Any ideas on how to tackle the stain? Have already tried
simple cleaning with garden furniture cleaner and then re-oiling, but
no joy. Have been reading about wood bleach and /or oxalic acid.
Anybody have experience of these?

TIA